An LTE/SAE (Long Term Evolution/System Architecture Evolution) system is a next-generation mobile communication system which has evolved from UMTS (Universal Mobile Telecommunications System) and aims at providing further improved mobile communication services.
The LTE/SAE system provides MBMS. MBMS is a further developed service which not only broadcasts multimedia data but also multicasts multimedia to users who subscribe to corresponding services. The MBMS provides, for example, a news channel, music channel, movie channel or the like.
As an MBMS transfer method in an LTE/SAE system, a method referred to as “single frequency network (“SFN”) transfer” is currently studied as a standard candidate. In an SFN transfer, a plurality of base stations belonging to the same SFN area are synchronized with each other across cells to transmit data regardless of the presence or absence of users, thereby improving received quality for the users through inter-cell diversity combining. The architecture and processing procedure of SFN transfer are disclosed in Non-Patent Documents 1, 2 and 3.
FIG. 1 shows an example of providing MBMS in the 3GPP (3rd Generation Partnership Project) LTE/SAE system. As shown in FIG. 1, one MBMS service area is formed with an SFN area where a service is provided through SFN transfer (Multi Cell Transmission: MCT) and a non-SFN area where a service is provided through multicast/unicast transfer other than the SFN transfer. Terminals (User Equipment: UE) receive the same service in any one of two different transfer modes, depending on to which area the terminals belong.
The operating mode of a UE is generally classified into the idle state and the active state. A UE in an idle state is managed by a core network (“CN”) in units of location registration areas, and the CN cannot identify to which cell in a location registration area the UE belongs. On the other hand, as for a UE in an active state, a radio communication base station apparatus (Evolved NodeB: eNB) and CN can identify the location of the UE in units of cells.
An MBMS allows services to be received in any of an idle state and active state, and a UE in an idle state can correctly receive desired MBMS by receiving MBMS control information broadcast by an eNB.
Next, a case where a UE in an idle state moves from an SFN area to a non-SFN area, will be explained using FIG. 2.
While receiving a certain service in an SFN area, the UE in an idle state performs cell reselection and moves from the SFN area to the non-SFN area (step (“ST”) 11).
Since a desired service is not constantly provided in the non-SFN area, the UE, which has detected that the service is not provided from MBMS control information broadcast by an eNB, transits to an active state and sends a MBMS reception request to a mobility management entity (“MME”) so as to request the CN to provide the service (ST12).
The MME having received the MBMS reception request executes MBMS bearer setting procedure between the eNB, to which the UE is connected, and a multicast user plane entity (“mUPE”), which provides the service, and establishes an MBMS bearer to provide the service (ST13).
Through ST13, the MBMS bearer to provide the service is established between the mUPE and the eNB, and the mUPE transfers the service requested by the UE to the established MBMS bearer (ST14).
When the non-SFN area supports unicast transfer, the MBMS bearer between the mUPE and the eNB in ST13 is a UE dedicated point-to-point (“PTP”) bearer, and, when the non-SFN area supports multicast transfer, the MBMS bearer is a point-to-multipoint (“PTM”) bearer common in the non-SFN area. When the UE moves within the non-SFN area, an MBMS bearer is reestablished for the destination eNB in any bearers.
Next, a case will be explained using FIG. 3 where a UE in an idle state transits to an active state and then moves from the SFN area to the non-SFN area. An eNB located on a boundary of the SFN area includes information indicating the boundary of the SFN area in broadcast information and transmits the result (ST21).
The UE in an idle state detects from the broadcast information that the UE is approaching the boundary of the SFN area, transits to an active state and sends an MBMS reception request to the MME (ST22), and the MME sets the requested MBMS bearer between the mUPE and eNB (ST23).
The mUPE transfers the service requested by the UE to the MBMS bearer, and the UE receives a desired service from the newly set MBMS bearer (ST24).
The UE in an active state normally measures received quality of neighboring cells and reports the measurement result to the eNB periodically or on an event-by-event basis. Here, suppose that the UE has moved to the vicinity of the boundary with a neighboring cell. The eNB, which has received the neighboring cell received quality measurement result reported from the UE, detects that the UE is located near the boundary with a certain neighboring cell.
The eNB instructs the UE to move to the detected neighboring cell, and the UE performs handover to the instructed neighboring cell (ST25).
When the handover is completed, the destination eNB sends a path switching request to the mUPE so as to switch the MBMS bearer established with the source eNB in ST23 to the destination eNB (ST26). The mUPE, which has received the path switching request, switches the MBMS bearer to the destination eNB, transfers the service desired by the UE to the switched MBMS bearer and the UE receives the service from the switched MBMS bearer (ST27).    Non-Patent Document 1: 3GPP TS 36.300 “3rd Generation Partnership Project; Technical Specification Group Radio Access Network, Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN), Overall description, Stage 2”, 2007-03    Non-Patent Document 2: 3GPP TR R3.018 “3rd Generation Partnership Project; Technical Specification Group Radio Access Network, Evolved UTRA and UTRAN, Radio Access Architecture and Interfaces”, 2007-02    Non-Patent Document 3: 3GPP TSG-RAN WG3#55 Tdoc R3-070063 “MBMS Service continuity when moving between SFN and non-SFN zones”, 2007-02